This proposal is directed toward morphological examination of brain parenchymal vessels under three conditons: physiologic, anoxia-ischemia (stroke) and subarachnoid hemorrhage. We plan to study the contraction and dilatation of brain parenchymal and pial vessels under conditions of hypocapnea, hypercapnea, hypotension and hypertension. Parenchymal vessel changes relative to concomitant pial vessel changes will be studied by means of a "pial window" technique which allows photography of pial vessels for measurement followed by immediate biopsy of the subjacent brain, freezing at -160 degrees C, sectioning and measurement of parenchymal vessel diameters. Other studies will be directed at parenchymal vessel changes following anoxiaischemia ("no-reflow phenomenon"). Brain will also be rapidly frozen for these studies and vessels will be examined morphologically and vessels will be examined morphologically and morphometrically. Electron microscopic studies of "no-fellow phenomenon"). Brain will also be rapidly frozen for these studies and vessels will be examined morphologically and morphometrically. Electron microscopic studies of "freeze-substituted" brain tissue will also be performed to analyze the smaller vessels. The effects of subarachnoid hemorrhage on both pial and parenchymal vessels will also be studied by the technique of rapidly freezing brain tissue after autologous blood has been introduced to the subarachnoid space.